1. Field of the Invention
The present invention relates to a semiconductor device including a sensor element made of vanadium oxide serving as a temperature sensor or an infrared sensor.
2. Description of the Related Art
Recently, temperature sensors have been introduced into a large scale integrated circuit (LSI) device to monitor the ambient temperature thereof (see: JP-1-302849-A). As a result, when the ambient temperature exceeds a normal temperature, a bias voltage applied to the LSI device is stopped to surely prevent the LSI device from being destroyed thermally due to the rise of the ambient temperature.
A first prior art temperature sensor is constructed by a temperature sensor element formed by a diode and a resistor having different temperature coefficients (also see: JP-1-302849-A).
In the above-described first prior art temperature sensor, however, since the temperature coefficient of the diode is so small that the difference in temperature coefficient between the diode and the resistor is small, a large signal-to-noise ratio (SNR) cannot be expected.
A second prior art temperature sensor is constructed by a temperature sensor element formed by a parasitic bipolar transistor or a parasitic pn diode (see: JP-9-229778-A). Since the parasitic bipolar transistor or the parasitic diode can be formed by a conventional MOS manufacturing process, the manufacturing cost can be decreased.
In the above-described second prior art temperature sensor, however, since the temperature coefficient of the parasitic bipolar transistor or the parasitic diode is still small, for example, about 0.2 (%/K), a large SNR cannot be expected.
A third prior art temperature sensor is constructed by a temperature sensor element made of vanadium oxide (see: JP-11-330051-A). Since the temperature coefficient of vanadium oxide is very large, a large SNR can be expected.
Note that stable vanadium oxide is represented by a chemical formula VO2 or V2O5, generally, VOX where X is about 2.
In the above-described third prior art temperature sensor, however, since a current is supplied to the vanadium oxide temperature sensor element, when an excessive current is supplied thereto, the vanadium oxide temperature sensor element would be broken down.
Also, JP-11-118567-A and JP-2003-121268—A disclose a bridge circuit including temperature sensor elements to enhance the sensitivity and a temperature detecting circuit connected to the two output terminals of the bridge circuit.
On the other hand, a prior art infrared sensor is constructed by an infrared sensor element made of vanadium oxide (see: JP-2001-0997-05-A). Since the temperature coefficient of vanadium oxide is very large, a large SNR can be expected.
Even in the above-described prior art infrared sensor, however, since a current is supplied to the vanadium oxide infrared sensor element, when an excessive current is supplied thereto, the vanadium oxide infrared sensor element would be broken down. Note that the above-mentioned infrared sensor is applied to an infrared camera formed by a plurality of infrared sensors to which pulse-shaped currents are supplied, In this case, if the number of pixels is so small that the vanadium oxide infrared sensor elements are large in size, such pulse-shaped currents supplied thereto hardly break down the vanadium oxide infrared sensor elements. On the other hand, if the number of pixels is so large that the vanadium oxide infrared sensor elements are small in size, such pulse-shaped currents supplied thereto would break down the vanadium oxide infrared sensor elements.